If an object such as a high wall or a handrail is installed along the far side of a target parking region (the side opposite to the side through which the vehicle enters the target parking region), that object will hinder parking.
For this reason, there are conventional parking assistance devices that determine whether or not an impeding object is installed along the far side of a target parking region, as in Patent Document 1.
With this parking assistance device, when the vehicle is caused to travel forward along the installation position of the target parking region at a time before the vehicle is to enter the target parking region, ultrasonic waves are emitted at a predetermined interval to the far side of the target parking region, and the distance to an object is measured.
As a result, reflection waves with a low projection height from the parking road surface, such as those reflected by a curbstone or the like, and reflection waves reflected by a wall or the like with a high projection height from the parking road surface are measured so as to determine whether or not a barrier exists.
Accordingly, the distance of an object at a low position, such as a curbstone, and the distance to an object at a high position, such as a wall, are compared, and if the difference between the respective distances to the objects is greater than or equal to a predetermined value, it is assumed that the object at the high position is at a position that is sufficiently further than the object at the low position, and it is not determined as a barrier for parking. On the other hand, if the difference in the distances to the objects is smaller than a predetermined value, it is assumed that a wall, a handrail, or the like exists near the curbstone or the like, and it is determined that an impeding object exists along the target parking region.